In a wireless charging system, a wireless power transmitting device such as a device with a charging surface wirelessly transmits power to wireless power receiving device such as a portable electronic device. The portable electronic device receives the wirelessly transmitted power and uses this power to charge an internal battery or to power the device.
It may sometimes be desirable to transmit data from the wireless power receiving device to the wireless power transmitting device. So-called in-band communications schemes have been developed that allow wireless power receiving devices to communicate with wireless power transmitting devices. In a typical in-band communications scheme, a switching circuit that is coupled to the coil in the wireless power receiving device is used to modulate the load across the coil. The wireless power transmitting device will attempt to detect the modulated signal using a sensing circuit coupled to a coil in the wireless power transmitting device.
The sensing circuit is powered by a power supply voltage. Ideally, the power supply voltage is a fixed signal that does not vary in time. In practice, however, the power supply voltage can exhibit power supply noise variation. Depending on its frequency, it is sometimes possible for the power supply noise variation to interfere with the in-band communications between the wireless power transmitting device and the wireless power receiving device. As a result, the reliability and the signal-to-noise ratio of the communications channel linking the wireless power transmitting device and the wireless power receiving device may be degraded.